Fate Shattered Destiny
by Avalon0117
Summary: Something interfere with the summoning of Shirou's servant, as a result he summoned a very different servant. And if there's something Shirou knows for sure about his partner for this Holy Grail War he is not a hero.
1. Chapter 1

**Hi everyone, this is my first fanfiction, it is a challenge from a friend of mine. I insist on this, it is my first fanfiction so please no flame. I might make some mistakes, and beside this is just a crazy plot bunny that is stuck in my head and that a friend told me to make into a fanfiction as a challenge.**

 **This will be based of Fate/Stay Night Unlimited Blade Works and Transformers Prime, it is set after the end of the TFP series and before the movie.**

 **Again this will be heavily AU so many things will be different.**

 **anyway, the disclaimer, I don't own anything.**

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 **Prologue:**

 **A Different Summoning**

Shirou's night couldn't have been worst, he had stayed late at school to do some repairs at school, and when he was finally about to leave he witnessed something he shouldn't have. Two strange men fighting one another, one clad in blue, and one clad in red. The blue one with the spear immediately chased after him. And killed him with just one stab of his spear through the redhead's heart,and yet, somehow, he had survived.

Shirou was home and trying to calm down and understand what happened and what had to do. Alas, fate wouldn't have any of that, the boy's eyes widened as he was alerted that someone had crossed the boundaries of the barrier around the Emiya residence. It was that blue spearman again.

After a brief fight that was completely one sided due to Lancer's superhuman abilities and the fact that Shirou didn't even have a proper weapon to fight with,The teenager was eventually cornered in the storehouse. he desperately looked around for anything that could possibly help him, meanwhile unnoticed by both him and Lancer who was about to finish him off ; a magic circle that had been there for years had started to shimmer mysteriously.

"End of the line boy! It is time die once and for all!" Lancer readied his spear making sure to aim properly so his next hit would provoke an instant death.

"No!I refuse to die!Not like this! Not befoe reaching my goal:becoming a hero of justice!" Shirou thought as the blood on his left hand shone a bright red before taking a shape vaguely reminiscent of a sword.

The circle finally activated reacting to the proximity of a master, at first the circle tried to find a catalyst to connect the new master to a servant, but it was disturbed by something, something interfered with the summoning , the circle became purple and suddenly released a blinding light.

Lancer barely had the time to dodge the incoming attack of the newly summoned servant.

"Tsk, really now? The seventh servant! How many more surprises do you have up your sleeves!" He barked angrily as he looked at the new servant.

He a very tall man, at least seven feet tall, muscular without a doubt, he wore a heavy set of armor made of steel that had clearly seen many fights, a purple decepticon insignia was on the middle of the chest-plate. The man's face was square and very angular, he had short silver hairs, a short boxed beard, but the most striking features were his eyes, two glowing blood red irises that shone with malevolence.

The weapon he wielded looked vaguely like a falchion but its blade was jagged and made of an unknown material some sort of dark purple crystal that shone eerily.

Shirou was starting to feel his heart beat heavily in his chest, there was something very wrong with the weapon his saviour had in his hands, it felt evil, he had never felt anything quite like this, he had never thought it was possible that traits like evil could apply to something that is not alive.

The man looked at Shirou with a sneer "I suppose you are my summoner? Make no mistake child, I won't be your disposable tool, though our fates are now tied together, for the moment..."

Then he turned around to face his opponent but choose to instead take a look at his body which caused him to show disgust "Bound to one of you organic weaklings...and forced to assumed the shape of your kind...how disgraceful" he said in a low growl as he readied his sword.

"I suppose you won't accept to call it a draw, won't you, Saber?" the blue lancer replied.

He scoffed "Certainly not, you are a danger that I must end now, I don't want you jeopardizing my plans later...and one more thing, I am not Saber" he replied coldly.

Lancer's eyes widened "Not Saber? Huh you are wielding a sword, how can you be anything else?!" he said shaking his head before taking a deep breath, his spear suddenly was engulfed in a red aura "It doesn't matter, you don't leave me much choice..." then he thrust his spear forward saying two words **"Gae Bolg!"**

At first it seemed like the new servant had blocked Lancer's attack, but then it somehow hit its target and sent him flying.

Lancer panted heavily and glared angrily as the new servant stood up again "Whoever you are, you are very lucky to have dodged my most powerful attack" he growled angrily.

The servant stood up, part of his chest plate had been torn and a visible bleeding hole was there showing that while having missed anything vital the spear had still hit its target.

"What...was that? A curse...no you reversed the cause and effect to hit me...you humans are really getting on my nerves!" he said anger obvious on his face, he grunted as he got back into a fighting stance his eyes began to glow with even more intensity, they seemed to be burning with hatred, as the warrior had a sudden surge of mana and attacked with an extreme speed and devastating strength.

Lancer was taken aback and barely dodged the attack and put some distance between him and his opponent "Y-you just had a surge of power after I harmed you?...hm so this is what you are...interesting, alas my master is a coward, he called me back since my attack failed...so see you next time...Avenger" he said before running away, or more precisely, jumping.

The now identified Avenger was about to go after Lancer but stopped as he was interpelled by his master, he sneered, he would never accept a puny organic as superior to him, and as such would not call the redhead this.

"Wait, what happened, and who are you?" Shirou asked obviously shocked and confused by what had happened in front of him.

Avenger stared at the boy with confusion obvious on his face "I am the Avenger-class servant you have summoned, you are the one who summoned me right?...of course you are, there is no one else around." Avenger said with a grunt " While you are there make yourself useful and heal my wound" he ordered, he had to set the ground rules as soon as possible, after all he couldn't let an inferior such as that human youngling think he could order him around.

"I-I can't, that level of magecraft is way beyond my abilities" Shirou replied getting more and more confused by the second, and he didn't like the tone the servant used .

Avenger was about to get angry over the lack of usefulness of the magus he was tied to, but he felt an alert trigger in his mind, another servant was approaching most likely with his master. "Looks like there's no time for talking, there's already another servant and their master approahing" He rushed toward the new threat, He managed to corner the master and servant, a tall man in red wielding two swords and a girl around the same age as his summoner, he smirked after hearing the girl calling her servant Archer, while he had swords, it meant that while his opponent had swords, he was mainly a long range fighter and potentially weak in close quarters.

Archer was completely taken aback when he saw this servant, he had expected Arthuria, but instead he was faced by a towering swordman who had absolutely nothing to do with her. Archer was about to change his tactic when Shirou arrived "Avenger stop it!" the youth cried out as the top part of the mark on the back of his hand flashed brightly before disappearing, Avenger gritted his teeth in cold fury as he was forced to obey the boy, that kid was starting to become a bigger liability with each second that passed."Thosaka-san, is that you?" the red haired boy asked before flinching from the murderous glare of his servant.

Rin nodded as she stood up and dusted her skirt. She smiled at Shirou "Well well, looks like we have much to discuss, don't we?Emiya-kun" she said with a playful smile.

 **End of the prologue**

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 **Servant sheet**

 **True identity:Megatron**

 **Class:Avenger**

 **Class skill:**

 **-Avenger A (representing the state of an Avenger as one that gathers people's hatreds and grudges onto oneself. It is easier for one to accumulate loathing and resentment. When receiving damage, mana generation is increased.)**

 **-Memory Correction (People are creatures that forget many things, but an Avenger never forgets)**

 **-Self-Replenishment B**

 **Personal skill:**

 **-Instinct B (Megatron's instinct had been honed through his fights in the gladiatorial pits of Kaon and during the war)**

 **-Charisma B (I need to justify this one? Megatron's charisma allowed him to raise an army to fight against the decrepit caste system )**

 **-?**

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 **I hope you liked it and I didn't rush it too much,this is my first fanfic again. . So of course all of you already know Avenger's identity , but nor Shirou nor anyone in Fuyuki know of his true identity hence why most of the time he will be referred to by his class.**


	2. Chapter 2

**Avalon0117:** **Hi hope you will enjoy this new chapter too, sorry for taking so long but I had a hard time thinking of a real plot with new interesting elements. I mean it is not hard for me to see how characters will interact but I don't want to do something that will be uninteresting being a complete copy of UBW's plot. And don't worry from now on since I know where I'm going with this story there will be updates more often.  
**

 **For those who follow between two worlds don't worry I am working on the next chapter it will arrive soon.**

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 **Chapter 1:**

 **Berserker**

Rin looked at the broken window, she inspected the glass shards and picked the biggest shard and whispered a quick incantation. The glass shards rose in the air and reassembled themselves fixing the window. Shirou watched the whole process with amazement, it had been a long time since he had since a display of magecraft such as this one.

"There good as new!" Rin exclaimed obviously proud of herself.

"Thanks Thosaka-san, this is great, I wouldn't have been able to fix it on my own" Shirou replied with a smile as he ran his hand along the perfectly smooth surface of the now fixed glass.

Rin looked at the redhead with shock obvious on her face, she was surprised that the boy wasn't able to do that "B-but that's the basic of basic! a fundamental!" she was truly surprised; that such a simple spell was something he couldn't do.

Shirou sighed "I can't do what you call the basics, I never learned the fundamentals. My father let me learn on my own.I never was much of a mage,my father on other hand, him, he was the real deal. The only magics I know are reinforcement and projection" he explained.

Rin's eyes widened even more as she heard that, and then a sudden and unpleasant shiver ran down her spine and that of Shirou as well. They looked around and found that the source of the unpleasant feeling was Avenger who was aiming his terrifying gaze at Shirou. The servant sneered at the children, more so at his incompetent master who was unable to do things that an another Master considered to be the basics.

Shirou smiled nervously, his servant was really unnerving "H-how about we move to the living room, it's kind of chilly here...,and I'll prepare some tea" he said.

Rin nodded slowly as she tried to disappear behind Shirou, suddenly Archer didn't seemed that bad .

When the three arrived in the living room, Archer was already there leaning against a wall, arm crossed. Megatron did the same leaning on the wall opposite to Archer, his gaze never leaving his summoner as he prepared this thing they called "tea", he didn't knew much about it beside the basics, and really didn't care about it , he sighed heavily, the grail shoved tons of useless data in his processor...brain, he corrected himself, it made him frown even deeper to remember he was now an organic by some sort of weird sorcery .

Once the tea was ready Shirou decided to offer some to Avenger hoping it would help the tension between them.

Megatron was about to refuse when Archer butted in with a remark "You should try, it work wonder for all kinds of tensions" he said with a chuckle.

Deciding there was no harm in doing so he accepted the cup with a grunt, the scent was oddly pleasant. he took a sip with some hesitation and found that it wasn't so bad, the taste although surprising was definitely enjoyable. His surprise was easily explainable, after all, no matter it's grade, no matter how you sweetened it, Energon was Energon, it's taste didn't change much. He kept sipping on his drink quietly while Shirou received a detailed explanation of what the Holy Grail War was. This drink really worked miracles for Megatron's anger issues, maybe that brat was good for something.

After the explanation Rin lowered her head "And to say that the one who get the Saber-class servant is someone who don't know even the basis of magecraft...a third rate magus!" she groaned

Then Shirou blinked in confusion decided to make a remark "Thosaka-san, I am not sure, but I think you made a mistake" he said glancing at Megatron "I summoned Avenger, not Saber" he said.

Rin's eyes grew comically wide "Avenger?! Impossible, there was only one! and it was back in the third Holy Grail War! the Einzbern family had created that special class trying to summon a unique servant but it failed spectacularly with their Avenger getting defeated on the fourth day of the war! Your servant was able to force Lancer to run and put up an impressive fight against Archer while wounded" she exclaimed.

Megatron grinned with malice obvious on his face, which caused Rin to shudder "Guess those Einzberns just made the wrong pick, but if you still doubt my abilities I could do a demonstration" if there was one thing this avenger liked , it was crushing those who underestimated him.

"N-no thanks!" the girl replied obviously unsettled by that grin that promised nothing but pain "A-anyway! I think Shirou needs to meet the mediator of this War to get a more precise idea of what he is in for"

Megatron nodded, it seemed a legitimate thing to do, so the group left for the church , both servant going into spirit forms which surprised Rin and Shirou but for different reasons "Wow...I wouldn't have thought Avenger would be able to go into spirit form , after all...you sort of summoned him in an improper way which should cause decreasing of parameters,inability to draw mana from the master, and of course the impossibility to use a spirit form..."

Shirou shivered expecting to get berated by his servant, but no such thing happened "The summoning was improper? Strange, everything is as the information given by the grail said..." Avenger remarked using the telepathic link he had with Shirou.

"Well, it's a good thing, at least even if I summoned you in a very unusual way you haven't suffered any negative effect from it" he replied getting a nod from his servant who observed as the two kids went into a church.

When they came out Megatron decided to speak to Shirou about the priest "Boy...there's something strange about this priest, I strongly advice you do not trust him."

Shirou was hesitant not too sure about this, Kirei was a strange person that was certain. But should he really be minding the extravagant priest this much"Why? sure he seemed a bit strange...but..."

Megatron sighed thinking of how to explain this to his master "There's something wrong in his eyes, in the way he speak and behave...that man is...I would say insane but...this doesn't cover it .He still is rational in his way of thinking, but his common sense is twisted. Those are the most dangerous kind of persons,they are completely unpredictable and you can never know for sure what they are truly thinking...and the worst part...is that he is the one overseeing this Holy Grail War"

That made Shirou shudder, if this Kirei was as mentally unstable as Megatron said he was, he could have been dragged into something even worst than he could imagine.

Rin was about to say something to Shirou and interrupt his telepathic conversation with Megatron when someone else did.

It was a small albino girl who seemed kind of cute at first glance but her innocent smile had something unsettling,like some sort of hidden malice. Shirou had seen her before, she had told him to summon his servant or he would die. "Hello Oni-chan"

Shirou took a step forward but was stopped by his servant"Stay away from her! she is a master!" Avenger shouted as he appeared and lunged at the girl with his sword that was blocked by what appeared to be a piece of stone crudely sculpted into an axe-sword hybrid. This barbaric weapon was held by the tallest human Megatron had ever seen. If this monster could be called human. About two meter and a half tall, and absurdly muscular, his skin was a very dark shade of gray and his black hairs looked like the raged mane of a savage beast. The monster easily shoved Avenger back as if he weighted nothing.

Rin didn't need help to identify the colossal servant "Berserker, the servant of madness..." she said as she readied her jewels "Looks like we'll have to fight together if we want to survive"she commented getting a nod From Megatron who got back into a battle stance. Archer materialized beside his master bow and arrow ready.

The little girl giggled mischievously "You don't have a single chance, you are facing the greatest hero of the Greek mythology, Heracles" she said with a proud smirk.

Megatron wasn't pleased by this situation, he had not expected that kind of opponent, his strength was incredible, this would be a difficult fight, it reminded him of his first fights in the gladiatorial pits of Kaon, facing enemies far stronger than him. It looked like he would be forced to reveal one of the tricks he had up his sleeves. And it annoyed him to do so while a future enemy was there. if Shirou had forgotten , Megatron hadn't. Rin Thosaka, while she was an ally at the present moment, she would be the next enemy the moment they no longer needed each other.

Megatron engaged a duel with the maddened greek hero, he quickly found he could barely keep the crazed beast at bay, each attack was only narrowly dodged, each furious swipe of the crude stone weapon missed the warlord by only a few inches, the pressure was unbearable, a single hit that would hit its mark could be fatal with the ridiculous strength of the rampaging creature he was facing. Archer managed to get a few good shots at the mad warrior thanks to openings created by the decepticon warlord who took risks to make them, but alas it didn't seem to do much, beside angering Berserker.

The decepticon warlord finally decided to use the trick he had kept in store. Megatron's veins began to glow through his skin an eerie purple color and his irises began to glow purple too, while the white surrounding them became pools of black tar. Shirou who was curious about what it was and focused on his servant's parameters and noticed that one of the skills that was previously concealed was now revealed, and so was the name of Avenger's weapon.

 **Personal skill:**

 **-Instrument of Unicron's will-Rank** **EX** (1)

 **Noble Phantasm:**

 **-Dark Star Saber, Wrath of Unicron (Rank EX, Anti-Divine)**

Shirou blinked at this "Unicron?" he asked to no one in particular, then he felt something, he felt his mana drained and pain, a pain that wasn't his own, this ability consumed an outrageous amount of mana but was also extremely harmful to the user draining him mentally and physically. Shirou couldn't keep up with the amount of mana needed especially using his nerves as mana circuits, the redhead lost consciouness from the pain that felt like his entire body was on fire. Meanwhile Megatron had begun to fight Berserker back with surprising efficiency having gained higher strength and speed, Ilya herself wasn't so confident anymore seeing the Avenger-class servant was actually fighting back now. The dark star saber had a sudden surge of purple energy and tore through the primitive stone battle-axe used by Berserker, and it slashed through the mighty warrior ripping his chest open.

Rin seemed content at first that the battle seemed to have turned in their favor, but she then noticed the state Shirou was in "Avenger! Stop that you are killing your master!" she shouted.

Megatron tsked out of annoyance as he had stop his assault, the glow from his veins died down and his eyes went back to their usual colors. He sighed, at least he was nearly done with this fight, or so he thought. Megatron was stunned as he saw Berserker's torn bloody flesh mend itself. Megatron began to panic internally, he had not expected this, and he was in no shape to fight since his use of Dark Energon left him barely able to move without it being painful "stupidly limited organic frame" he growled under his breath.

Archer disappeared in a burst of speed as he saw that this was useless and that they needed to do something more...drastic. Megatron didn't have the time to ask himself what the servant of the bow had in mind as he had to survive against the furious and continuous assaults of Heracles who was now back to full strength, the situation was getting desperate as he could barely keep up anymore, narrowly dodging fatal blows that while missing their target still managed to damage him. Then the decepticon warlord felt an alarm trigger in his mind, something extremely dangerous was closing in. In a burst of speed he grabbed both Shirou and Rin and took them as far as he could from Berserker who was hit by what seemed to be an arrow, but the resulting explosion reminded Megatron of a missile.

"That Archer of yours is far stronger than what I have imagined..." Megatron said as he gazed at the burning crater left by the impact of the caladbolg arrow. His stoic expression soon turned in one of pure horror, there in the middle of the burning and smoking crater stood Heracles, still alive and fully regenerated "By the Pits! What's that, regeneration? No...not like that,no...at such level, it has to be some sort of revival...but how?"

Ilya was not too far from Berserker and chuckled "See I told you that you couldn't win against Berserker, still both of you Archer and Avenger impressed me...so I'll let you live, for now" she said with a cute smile that barely concealed the malevolence beneath it, she then left with her servant walking by her side.

Megatron huffed, for such a young human she was almost scary, almost being the keyword. "I suppose we should go back to the base to get some rest" he said looking at Shirou who was unconscious.

Rin nodded "Yes it would be a good idea considering I need to know the amount of harm your little stunt caused to Shirou" she said obviously both worried and angry.

Megatron ignored the remark merely ticked off that he had to compose with not only the limits of an organic body but also his summoner's own frailness. And now he had to carry his unconscious master home. Really human's were useless and pathetic creatures, he didn't knew how long he could put up with these annoyances.

 _The next morning_

When Shirou woke up, he was greeted by the sound of a discussion between Megatron and Rin, obviously the girl had not liked one little bit how the warlord recklessly endangered his master's life. « Really what did you have in mind ! Whatever you did siphoned Shirou's mana far too fast ! It could have killed him ! »

But nothing she could say seem to actually have any impact on the leader of the Decepticons , which ended up frustrating her even more, but she eventually gave up seeing the former gladiator was ignoring her. then she noticed that the red head had regained his consciousness.

"Well, well you are finally awake. You are really lucky to be alive, you should be dead seeing the damages caused by the large amount of mana you servant used..." the red clad magus said as she looked at Shirou with concern.

the boy rubbed the back of his neck "Yeah, Guess that was too much for my nerves..." he said with a chuckle.

Rin's eyes widened with disbelief "YOUR NERVES! You use your nerves instead of your magic circuits!" she shouted obviously furious, which had Shirou back away in fear "What did that father of yours teach you! This is dangerous!"

Shirou sighed "My father never explained me that I wasn't supposed to do that, I was never really trained as you already know" he replied.

Rin facepalmed and shook her head "Looks like I'll have to show you how to properly access your magic circuits." she said with a heavy sigh.

Shirou blinked and looked at Rin with confusion obvious in his eyes "You said we would be enemies from today on , why are you helping me?" he asked.

Rin chuckled "Well , we are having an...let's say truce, me and Avenger talked about it,we agreed we had to join forces until Berserker is defeated...after that we'll be enemies again" she answered becoming serious again when saying the last part "It's not like I really care about you" she added looking away with a faint blush.

Megatron and Archer both scoffed while thinking _"pff femmes/women..."_ they obviously had both seen right through Rin, which was not too hard considering the way she reacted or rather overreacted over what happened to a supposed "temporary ally" being in danger. She fooled Archer even less since he had seen his master using one of her most powerful jewels to save Shirou, you just don't do something like that for a temporary ally that will become your enemy later.

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(1) _Servant_ _Profile_ _Update_

- **Instrument of Unicron's will - rank EX** : represent the state of one who has tainted the very essence of their existence with the blood of the God of Destruction ,to the point where they became a suitable vessel for him. this skill represent the highest form of the skill [Blood of Unicron]. For example Star Scream who used Dark Energon at one point in his life, if he could be summoned, would have an E-rank version of this skill which wouldn't do much.

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 **There hope you all enjoyed this chapter, don't forget to comment and tell me what you liked, and also leave any constructive critics you may have.**


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